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FUNCTION Component of the 9-1-1 cell-cycle checkpoint response complex that plays a major role in DNA repair (PubMed:10713044, PubMed:17575048, PubMed:20545769, PubMed:21659603, PubMed:31135337). The 9-1-1 complex is recruited to DNA lesion upon damage by the RAD17-replication factor C (RFC) clamp loader complex (PubMed:21659603). Acts then as a sliding clamp platform on DNA for several proteins involved in long-patch base excision repair (LP-BER) (PubMed:21659603). The 9-1-1 complex stimulates DNA polymerase beta (POLB) activity by increasing its affinity for the 3'-OH end of the primer-template and stabilizes POLB to those sites where LP-BER proceeds; endonuclease FEN1 cleavage activity on substrates with double, nick, or gap flaps of distinct sequences and lengths; and DNA ligase I (LIG1) on long-patch base excision repair substrates (PubMed:21659603). The 9-1-1 complex is necessary for the recruitment of RHNO1 to sites of double-stranded breaks (DSB) occurring during the S phase (PubMed:21659603). RAD9A possesses 3'->5' double stranded DNA exonuclease activity (PubMed:10713044).CATALYTIC ACTIVITY Exonucleolytic cleavage in the 3'- to 5'-direction to yield nucleoside 5'-phosphates.SUBUNIT Component of the toroidal 9-1-1 (RAD9-RAD1-HUS1) complex, composed of RAD9A, RAD1 and HUS1 (PubMed:10359610, PubMed:10777662, PubMed:10846170, PubMed:10884395, PubMed:15314187, PubMed:15556996, PubMed:15871698, PubMed:15897895, PubMed:16216273, PubMed:17575048, PubMed:20545769, PubMed:31135337). The 9-1-1 complex associates with LIG1, POLB, FEN1, RAD17, HDAC1, RPA1 and RPA2 (PubMed:10884395, PubMed:15556996, PubMed:15871698, PubMed:15897895, PubMed:16216273). The 9-1-1 complex associates with the RAD17-RFC complex (PubMed:12578958). RAD9A interacts with BCL2L1, FEN1, RAD9B, ABL1, RPA1, ATAD5 and RPA2 (PubMed:11971963, PubMed:12628935, PubMed:14500360). Interacts with DNAJC7 (PubMed:11573955). Interacts (when phosphorylated) with TOPBP1 (PubMed:17575048, PubMed:20545769, PubMed:31135337).INTERACTION Constitutively phosphorylated on serine and threonine amino acids in absence of DNA damage (PubMed:12628935). Hyperphosphorylated by PRKCD and ABL1 upon DNA damage (PubMed:11971963, PubMed:12709442). Its phosphorylation by PRKCD may be required for the formation of the 9-1-1 complex (PubMed:12628935). Phosphorylated at Ser-341 and Ser-387 by CK2, promoting interaction with TOPBP1 (PubMed:17575048, PubMed:20545769).SIMILARITY Belongs to the rad9 family.
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